The present invention relates to methods for producing polycrystalline diamond compacts made by high pressure/high temperature processes (HP/HT), and more particularly to a method whereby the ability to reliably detect flaws in polycrystalline diamond masses when using x-ray imaging techniques is improved. This invention has special application with respect to supported polycrystalline diamond wire die compacts.
A polycrystalline diamond wire die compact comprises a mass of polycrystalline diamond which mass is then pierced to enable wire to be drawn through it. The polycrystalline diamond mass comprises diamond particles bonded one to another to form an integral, tough, coherent, high strength body typically having a diamond concentration of at least seventy (70) volume percent. The formation of extensive diamond-to-diamond bonds between the particles is achieved using a sintering aid such as cobalt. While such diamond masses can be directly attached to a holding fixture, they are typically and conveniently produced integral with a surrounding annular support of metal bonded carbide such as cobalt cemented tungsten carbide. Representative conventional polycrystalline diamond wire die compacts are disclosed, for example, in U.S. Pat. Nos. 3,831,428, 4,129,052, and 4,144,739.
While such diamond compacts may be produced from a range of diamond particle sizes, the ease of finishing diamond wire dies that have been sintered from fine grain diamond, e.g., less than about 10 microns, and the improved surface finish of wires that have been drawn through such dies make fine grained diamond compacts especially desirable in the marketplace. This is noted, for example, in U.S. Pat. No. 4,370,149.
Although polycrystalline wire die compacts offer a number of advantages, their production has been difficult due to unacceptable incidents of flaws in the diamond cores. The incidence of flaws during fabrication tends to increase with the size of the polycrystalline mass and as the diamond feed size decreases. It has been suggested that the addition of particles of other materials designed to inhibit excessive regrowth during the formation of diamond-to-diamond bonds can account for some improvement in producing flaw-free diamond masses. Hara et al., "On the Properties of Fine Grain Sintered Diamond Bodies," Proceedings of the 10th Plansee-Seminar, Hugo M. Ortner, Editor, Metal Work Plansee, Reutte, Austria, Vol. 2, pp. 581-589 (1981). Another technique proposed to improve the diamond compact portion of the wire drawing dies is the use of additives, such as boron, tungsten carbide, and the like, as set forth in U.S. Pat. Nos. 3,913,280, 4,268,276, 4,370,149, and South African Application No. 756730.
Yet another approach is the so-called "axial infiltration" technique as disclosed in commonly-assigned application of Cho, U.S. Ser. No. 313,119, filed Oct. 20, 1981, now U.S. Pat. No. 4,534,934. This technique involves the placement of a source of a catalyst/solvent sintering aid on one axial end of a diamond mass to be sintered followed by application HP/HT. While such improvements are helpful, it remains vital to accurately detect those flaws which do occur.
Flaws that develop in the production of polycrystalline diamond compacts which are of particular concern include poorly or non-uniformly bonded zones characterized by a lower hardness than non-flawed areas. They can result from a high or low concentration of sintering aid which can lead to a lesser amount of diamond-to-diamond bonding. Flawed zones can exhibit a different coloration from the non-flawed areas or a different texture. Flaws near the surface of polycrystalline diamond compacts are often detectable visually and can normally be remedied by lapping or other mechanical means. Flaws within a polycrystalline mass are more difficult to detect. Moreover, since the interior of a wire die performs the wire drawing operation, internal flaws are especially critical in a polycrystalline diamond wire die compact. Consequently, methods for accurately and reliably detecting or sensing such flaws or poorly bonded zones is quite important to both the manufacturer of the polycrystalline diamond wire drawing dies as well as for the users of such dies.
Present day practice involves the use of x-ray radiographs of the diamond wire die compacts in order to detect internal flaws. It is an object of the present invention to provide a compact which will enable an increase in the ability to reliably detect flaws using such conventional x-ray techniques.